I am using Asim Khan's Parallel port Programmer to program my AVR ATmega8 controller. The Problem is when I changes fuse bits to external high speed crystal, then the next time programmer does not detects the programmer. I am really frustrated to figure out what would be the problem. Can any one helps me to locate the problem? Thanks in advance
Assuming you set the correct fuses, the crystal may not start oscillating because of wrong feedback capacitor values. The "correct value" depends on the load capacitance of the crystal.
- you have properly connected external feedback capacitors
- the capacitors have the recommended value (refer to uC and crystal data sheets)
- the PCB traces are as short as possible (long traces introduce a parasitic capacitance and high impedance)
- try setting CKOPT fuse (from mega8 data sheet: "When CKOPT is unprogrammed, the Oscillator has a smaller output swing. This reduces power consumption considerably. This mode has a limited frequency range...")